9

Point-Point Constraint 751
reactor also provides two variations on the
Point-Point constraint: Limited and Stiff Spring.
With a Limited Point-Point constraint, you can
specify limits for how much the child object
canrotaterelativetotheparent. AStiffSpring
constraint is similar to a standard Point-Point
constraint with one important exception: It
holds the constrained bo dies apart at a specified
distance, as if they were attached at each end of an
invisible rod. The Stiff Spring variant requires a
point in the body space of e ach of two bodies, and
a constant distance by which reactor must keep
these two points sep arated. Each b ody is free to
rota te around its point.
The constraint is simulated w hen it has the correct
numberofrigidbodiesattachedandisincludedin
avalidConstraint Solver (page 2–736).Whennot
selected, an invalid Point-Point constraint is red in
the viewpor t.
Pr ocedur es
To create a Point-Point constra int:
• Chooseoneoftheaboveoptions,andthen
click in any viewport to add the Point-Point
constraint.
Note: The icon’s position has no effect on the
constraint’s behavior.
To attach objects to the Point-Point constraint:
1.
Create the constraint and the objects to connect
with it.
2. Ontheconstraint’sPropertiesrollout,clickthe
Childpickbutton,andthenselecttheobjectto
use as the child object in one of the viewports.
By default, this attaches the constraint to the
body at the body’s pivot point.
3. If you do not want to assign a second body to
the constraint, turn off the Parent check box
if necessary.
4. If the constraint is to be two-bodied, make
sure Parent is on and then use the Parent pick
button to set the parent for the constraint. By
default, the attachment point for the pa rent is
also alig ned with the child b ody’s pivot point,
which means that the bodies will maintain their
current positions relative to each other in the
simulation.
To create the constra int a nd a ttach objects in a single
step:
•SeetheScripts (page 2–817) topic.
To change the a ttachment positions for the bodies:
1.
With the constraint selected, open the Modif y
panel.
2. In the modifier stack open the constraint’s
sub-object list.
3. Access the sub-object level corresponding to
the object in whose space you want to move
the attachment point: Parent Space or Child
Space. If the constraint is single-bodied, Parent
Spaceallowsyoutomovetheworldattachment
position.
4. The corresponding point becomes active in the
viewports and can b e moved using the Move
tool.
The attachment point maintains its posit ion
relative to its corresponding object. For
example, if you move the child object, its space,
and hence its attachment point, moves with it.
Theattachmentpointdoesn’thavetoactually
be on either object.
5. To reset the attachment point to the child
object’s pivot, reattach the objects to t he
constraint, or click the Alig n Spaces To > Child
Body button.
To limit the rotation between the attached objects:
1.
With the constraint selected, open the
Properties rollout.